In the production of zinc from zinc ores, the current procedure is typified by that described beginning on page 183 of the 1959 book by C. H. Mathewson entitled Zinc--the Science and Technology of the Metal, Its Alloys and Compounds. At page 183, the recovery technique currently used at many places is described. In the flow chart exemplified at FIG. 6-12 of that text, electrolizing cells are provided with a filtrate of zinc in acid solution. The typical concentration heretofore provided has been in the range of about 70 grams per liter. The process heretofore has removed about 10 grams per liter of zinc or about 14%. It has also reconstituted about 15 grams per liter of sulfuric acid. The outflow after processing has been approximately sixty grams per liter of zinc remaining in solution typically as zinc sulfate mixed with some reconstituted sulfuric acid. The outflow has been recycled to the leach step with some added ore concentrates so that the process is repeated in cyclical fashion with feedback on a continuous operation basis. It is apparent that the bulk (about 85%) of the purified feed stock is recontaminated on its return to the leaching step. The ineffeciency of the process has been overcome by this invention.
An examination of the approximate rates of removal mentioned above illustrates amply the excessive cost of this process. The cost is excessive because only about 14% of the zinc is recovered at the electrolyzing step. When the electrolyzing step is completed, approximately 86%, more or less, must be recycled or completely reprocessed through the various leaching and filtration steps. The limits on process efficiency result from the acid attack on the plated zinc. The zinc is redisolved into solution when the acid is too strong. One limit on the process is the existence in the electrolyte of different organic chemicals in solution or suspension that either carry electrical charges, or as electrically neutral molecules in the waters of hydration.
It has been discovered that the electrolyzing cell can be modified and a new technique of removal of the zinc from the zinc sulfate solution is disclosed. The method of this disclosure is particularly advantageous in that it is substantially more efficient. Instead of removing only about 14% in a typical situation, it differs in that it cooperates with the supply of zinc sulfate having a concentration of up to about 200 grams of zinc per liter. It removes up to about 95% of the zinc leaving about 10 grams per liter in the discharge from the new and improved removal cell disclosed herein. Thus, rather than recycle up to about 86% of the zinc originally supplied to the removal apparatus, only about 5% of it is recycled. This either reduces the size of the refining apparatus or enables the handling of substantially larger volumes of zinc ores at a given refinery. In any case, the volumes recycled through the method of this invention are substantially reduced thereby resulting in a reduction in cost to the apparatus and a streamlining of the production facility. The improved recovery rate is partly a result of the separation of respective ions into their respective electrode chambers by the process of stripping these ions of their waters of hydration; which waters of hydration can contain pollutants which interfere with the electrolytic process.